1. Field of the Invention
The present invention is directed in general to digital radio broadcast receivers and methods for operating same. In one aspect, the present invention relates to methods and apparatus for recovering digital signal information at a radio receiver.
2. Description of the Related Art
Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers using existing radio bands. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital radio broadcasting, transmits digital radio and analog radio broadcast signals simultaneously on the same frequency using digitally modulated subcarriers or sidebands to multiplex digital information on an AM or FM analog modulated carrier signal. HD Radio™ technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception. With IBOC digital radio broadcasting, signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers or in an all-digital format wherein the analog modulated carrier is not used. In the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog-to-digital radio while maintaining their current frequency allocations. Another feature of IBOC digital radio broadcasting is the digital transmission capability to simultaneously transmit both digitized audio and data so that one or more digital audio programs can be broadcast within a single logical channel, alone or in combination with wireless data messages, such as metadata (e.g., the artist, song title, or station call letters), special messages (e.g., event, news, traffic, and weather information), or other message information that can all be scrolled across a radio receiver's display while the user listens to a radio station. Of course, with any wireless or radio-based communication system, there are potential signal errors and distortions that arise from the adverse channel conditions which can affect or disrupt signal detection at the receiver. While error detection and correction mechanisms can be used in the signal decoding process, such mechanisms typically do not provide the ability to recover transport elements within a frame (e.g., packet boundaries within the frame) if there are errors in the frame header. As a result, digital signal decoding errors can result in prolonged signal blending from digital to either analog signal or to silence. Accordingly, the present inventor has found that a need exists for improved method and apparatus for processing the digital audio signals to overcome the problems in the art, such as outlined above. Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.